have cursor ignore vive-controls/custom touchstart events

Author: ngokevin

src/components/cursor.js

@@ -183,6 +183,9 @@ module.exports.Component = registerComponent('cursor', {
       var point;
       var top;
 
+      // Ignore custom events (e.g., `vive-controls` touchstart).
+      if (!evt.isTrusted) { return; }
+
       camera.parent.updateMatrixWorld();
       camera.updateMatrixWorld();